Dishwashers have become an integral part of everyday household use. Consumers place dishware and other utensils onto dishwasher racks inside dishwashers for cleaning. Dishwashers typically clean the dishware with wash systems that utilize spray arms and spray jets to propel water and/or wash fluid onto the dishware to remove food particles and otherwise clean the dishware.
Dishwashers typically comprise a sump in the base of the dishwasher tub. The wash fluid in the dishwasher runs down inside of the dishwasher tub and collects in the sump. A circulation pump then recirculates the collected wash fluid through one or more spray arms inside the dishwasher. For the circulation pump to efficiently recirculate the wash fluid, it is important to prevent air and/or vapor from entering the pump (i.e., starving or cavitating the pump). Therefore, during operation, the inlet of the circulation pump is fully submerged (e.g., covered) by a minimum level of wash fluid to ensure that air and/or vapor doesn't enter the circulation pump inlet.
Energy and water conservation is important and, thus, there is a desire to reduce the amount of water used in dishwashers. However, simply reducing the amount of water used by a dishwasher reduces the amount of wash fluid available for sufficiently submerging the inlet to the circulation pump. As noted above, if the fluid level at the circulation pump inlet is not sufficient, the circulation pump will starve to some degree, causing the circulation pump to work inefficiently and/or fail. Indeed, in some cases, a large volume of wash fluid is needed to ensure that the fluid level at the circulation pump inlet remains sufficient at all times during operation. This is due to the fact that, during operation, wash fluid may be spread throughout the dishwasher tub (e.g., in the circulation system, in the spray arms, in upside down dishware, running down the dishwasher tub, etc.). In some embodiments, the fluid height at the pump inlet can provide the pressure necessary at the circulation pump inlet to prevent cavitation by keeping the pressure along the blades of the impeller above the vapor pressure. Increased fluid height at the circulation pump inlet also helps to avoid the formation of vortices in the fluid that can draw vapor down into the pump inlet, a process called carry under. These vortices can be formed where fluid acceleration into and near the circulation pump inlet is relatively high and the available pressure, due to fluid height, is not sufficient to prevent the vapor from being drawn down into the fluid. As the fluid height increases the buoyant force available for lifting vapor up through the fluid to escape or to prevent it from being drawn down into the wash fluid to the circulation pump inlet is increased. The actual volume of wash fluid necessary to achieve the required fluid height is dependent upon the geometry below the fluid level, especially that of the sump and tub.
In a dishwasher, the wash fluid is sprayed onto the dishware by one or more spray arms. The wash fluid then drips off the dishware and/or runs down the sides of the tub to the bottom of the tub and into the sump. Due to the nearly infinite number of possible dishware configurations within the dishwasher, the flow of the wash fluid into the sump of the dishwasher is difficult to predict. In this regard, air may enter the fluid returning to the pump in a variety of ways. This includes at least the aeration that may occur as fluid passes through a filter mesh and the entrainment of air in the fluid due to the capture of air during unbounded flow, as in the case of flow over an obstruction like a rib or ledge or the crashing of waves droplets or streams into the fluid surface. Wash fluid flowing from different parts of the tub tends to carry various angular and linear momentums in various directions, resulting in a turbulent flow. The turbulence of the fluid flow can pull air downwards and thus works against the natural buoyant forces that would otherwise cause the air to rise up and out of the fluid. Turbulence may also result in fluid momentum in directions that are opposed to what the circulation pump is designed to create and that are, by definition, not the preferred, laminar flow. Turbulent flow may also contribute to the creation of vortices that pull air and/or vapor down into the pool at the circulation pump inlet, increasing the air and/or vapor passing through the circulation pump. Unsteady and turbulent flow can also result in an uneven fluid surface height with the low points being more susceptible to the creation of vortices that can cause carry under.